Air‐gun bubble damping by a screen

Geophysics ◽  
1995 ◽  
Vol 60 (6) ◽  
pp. 1765-1772 ◽  
Author(s):  
Jan Langhammer ◽  
Martin Landrø ◽  
James Martin ◽  
Eivind Berg
Keyword(s):  
Near Field ◽  
Field Measurements ◽  
Far Field ◽  
Pressure Amplitude ◽  
Air Bubble ◽  
Air Gun ◽  
Pressure Peak ◽  
Bubble Oscillations ◽  
Measured Pressure ◽  
Optimal Radius

A method for damping unwanted bubble oscillations from a seismic air gun is presented. The method exploits the fact that the primary pressure peak generated by an air gun is produced during the first 5–10 ms after firing. The air bubble is destroyed by mounting a perforated screen with an optimal radius about the gun. Once the primary pressure peak has been generated by the bubble, the bubble is destroyed by the screen, leading to a corresponding decrease in the measured pressure amplitude of the secondary bubble oscillations. Controlled near‐field measurements of 40‐cubic inch and 120‐cubic inch air guns with and without damping screens are used. The primary to bubble ratio improves from 1.4 without a screen to 4.4 with a screen in the near‐field. The corresponding values for estimated far‐field signatures are 1.8 to 9.0 when the signatures are filtered with an out‐128 Hz (72 dB/Oct) DFS V filter.

Damping of secondary bubble oscillations for towed air guns with a screen

Geophysics ◽  
1997 ◽  
Vol 62 (2) ◽  
pp. 533-539
Author(s):  
Martin Landrø ◽  
Jan Langhammer ◽  
James Martin
Keyword(s):  
Near Field ◽  
Far Field ◽  
Pressure Amplitude ◽  
Air Bubble ◽  
Air Gun ◽  
Pressure Peak ◽  
Bubble Oscillations ◽  
Measured Pressure ◽  
Optimal Radius ◽  
Boat Speed

A method for damping unwanted bubble oscillations from a horizontally towed seismic air gun is presented. The air bubble is destroyed by a perforated screen mounted at an optimal radius about the gun. Once the primary pressure peak has been generated by the emerging bubble, the bubble continues to expand and is destroyed by the screen, leading to a corresponding decrease in the measured pressure amplitude of the secondary bubble oscillations. For a stationary gun fired first without, and then with, the screen fitted, the primary‐to‐ bubble ratio improves in the near field from 1.7 to 5.2, respectively, at a firing depth of 3 m and from 1.5 to 5.5, respectively, at 5 m depth. The primary‐to‐bubble ratio for a towed air gun in the quasi‐far‐field improves from 2.0 to 11.0 at 4 m depth and from 1.5 to 8.7 at 7 m depth when the screen is fitted. The boat speed was 1.6 knots and the signatures were filtered with an out‐128 Hz (72 dB/Oct) DFS V filter.

Single water gun far‐field pressure signatures estimated from near‐field measurements

Geophysics ◽  
1985 ◽  
Vol 50 (2) ◽  
pp. 257-261 ◽  
Author(s):  
M. H. Safar
Keyword(s):  
High Resolution ◽  
Data Acquisition ◽  
Seismic Data ◽  
Near Field ◽  
Field Measurements ◽  
Reference Source ◽  
Far Field ◽  
Air Gun ◽  
Seismic Data Acquisition ◽  
Marine Seismic

An important recent development in marine seismic data acquisition is the introduction of the Gemini technique (Newman, 1983, Haskey et al., 1983). The technique involves the use of a single Sodera water gun as a reference source together with the conventional air gun or water gun array which is fired a second or two after firing the reference source. The near‐field pressure signature radiated by the reference source is monitored continuously. The main advantage of the Gemini technique is that a shallow high;resolution section is recorded simultaneously with that obtained from the main array.

On: “The signature of an air gun array: Computation from near field measurements including interactions” by A. Ziolkowski, G. Parkes, L. Hatton, and T. Haugland (GEOPHYSICS, v. 47, p. 1413–1421, October, 1982).

Geophysics ◽  
1984 ◽  
Vol 49 (11) ◽  
pp. 2067-2068
Author(s):  
M. H. Safar
Keyword(s):  
Hydrostatic Pressure ◽  
Dynamic Pressure ◽  
Near Field ◽  
Field Measurements ◽  
Air Bubbles ◽  
Surrounding Water ◽  
Radiation Impedance ◽  
Air Bubble ◽  
Air Gun ◽  
Third Law

I would like to make two comments regarding the discussion on interaction between air bubbles given by Ziolkowski et al. The first concerns their statement that their approach for treating interaction is exactly the same as my approach (Safar, 1976), namely, that interaction is treated as a modulation of the hydrostatic pressure just outside the air bubbles. I would like to emphasize that, in fact, this was the approach used by Giles and Johnston (1973) and not the approach that I used in my paper. Since the problem of interaction between seismic sources forming an array is of considerable importance from the operational viewpoint, I give a summary of the analysis which I gave in my paper. Consider the case of two identical air guns placed at the same depth. When only one gun is fired, one air bubble is produced. From Newton’s third law, the effective pressure acting on the pulsating air bubble is not equal to the hydrostatic pressure as was stated by Ziolkowski et al., but equal to the hydrostatic pressure [Formula: see text] plus the dynamic pressure exerted by the surrounding water which is given by [Formula: see text], (1) where the dot denotes differentiation with respect to time t, v(t) and [Formula: see text] are the air bubble instantaneous volume and radiation impedance.

On: “The signature of an air gun array: Computation from near‐field measurements including interactions”, by A. Ziolkowski, G. Parkes, L. Hatton, and T. Haugland (GEOPHYSICS, 47, p. 1413–1421.)

Geophysics ◽  
1983 ◽  
Vol 48 (9) ◽  
pp. 1293-1293
Author(s):  
Erhard Wielandt
Keyword(s):  
Near Field ◽  
Field Measurements ◽  
Air Gun ◽  
Pressure Term ◽  
Flow Pressure ◽  
Bubble Oscillations

I wish to put forward a few arguments in favor of the after‐flow pressure term which Keller and Kolodner (1956) retain in their calculation of bubble oscillations and which Ziolkowski et al consider as “absolutely negligible.”

The signature of an air gun array: Computation from near‐field measurements including interactions—Practical considerations

Geophysics ◽  
1984 ◽  
Vol 49 (2) ◽  
pp. 105-111 ◽  
Author(s):  
G. E. Parkes ◽  
A. Ziolkowski ◽  
L. Hatton ◽  
T. Haugland
Keyword(s):  
Pressure Field ◽  
Near Field ◽  
Field Measurements ◽  
Weather Conditions ◽  
Normal Operation ◽  
Far Field ◽  
Iterative Technique ◽  
Forward Motion ◽  
Air Gun ◽  
Bad Weather

We have refined our system for calculating the signature of an interacting air gun array from near‐field measurements of its pressure field. We use an iterative technique to calculate a notional array of noninteracting sources from the near‐field hydrophone measurements. The notional signatures form the basis for calculating the array signature in any direction. The success of our iterative technique depends upon prudent positioning of the hydrophones, one close to each air gun. In normal operation the forward motion of the hydrophones and upward motion of the air gun bubbles are important effects which must be included in the equations. A linear model for this motion is adequate and improves the method significantly. The vertically traveling “far‐field” signature calculated by our extended method matches an equivalent “far‐field” measurement very closely. We present array signatures obtained in very bad weather conditions (force 8). In this extreme test the signatures are very stable from shot to shot. Therefore it is not necessary to calculate the array signature every shot; however, continuous recording of near‐fields should still be carried out as a check on signature stability.

Antenna Far Field Reconstruction by a Minimum Near Field Measurements

1984 ◽  
Author(s):  
G. D'Elia ◽  
G. Leone ◽  
R. Pierri ◽  
G. Schirinzi
Keyword(s):  
Near Field ◽  
Field Measurements ◽  
Far Field ◽  
Field Reconstruction
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